Test the two gestures the rework is actually about

The browser suite checked what the app renders but nothing about authoring,
which is the part that changed. It now registers a fresh account and walks
the wizard, including the case where a partner added mid-wizard has to appear
by name without navigating away first, and it drags a range on the calendar,
deletes the period, and reloads to confirm the days really went. Both are
regressions that were found by hand within the last day and would have been
found here instead.

Doing this surfaced that the age-four spec had been asserting on figures that
moved inside a collapsed section, so it had stopped checking anything. The
stale note about the retired tips page went too.

frontend/e2e/support/calendarNav.ts

@@ -21,3 +21,44 @@ export async function goToCalendarMonth(page: Page, date: Date): Promise<void> {
 export function calendarDayCell(page: Page, isoDate: string) {
   return page.locator(`[data-testid="calendar-day"][aria-label^="${isoDate}"]`)
 }
+
+/**
+ * Drives a real drag-select across the given ISO dates (in order), the way
+ * `Calendar.tsx` expects it: `CalendarDay` wires plain `onPointerDown`/
+ * `onPointerEnter` handlers (see `CalendarWeek.tsx`), and the page only
+ * treats the gesture as a multi-day drag if `pointerenter` actually fired
+ * for every intermediate cell before `pointerup` — see the `dates.length
+ * === 1` branch in `Calendar.tsx`'s `pointerup` handler, which opens the
+ * single-day modal instead of creating a period.
+ *
+ * A single fast `mouse.move` (or Playwright's default `hover()`/`dragTo()`)
+ * can collapse into one native pointer event and skip the intermediate
+ * cells entirely, which reads as a click on the anchor date. Moving in
+ * several steps per cell, with a short pause between cells, is what
+ * reliably fires a `pointerenter` on each one.
+ */
+export async function dragSelectDates(page: Page, isoDates: string[]): Promise<void> {
+  if (isoDates.length < 2) {
+    throw new Error('dragSelectDates needs at least two dates to actually drag across')
+  }
+
+  const centerOf = async (isoDate: string): Promise<{ x: number; y: number }> => {
+    const box = await calendarDayCell(page, isoDate).boundingBox()
+    if (!box) throw new Error(`calendar day cell not visible for ${isoDate} — is it in the current month view?`)
+    return { x: box.x + box.width / 2, y: box.y + box.height / 2 }
+  }
+
+  const [firstDate, ...restDates] = isoDates
+  if (!firstDate) throw new Error('dragSelectDates needs at least two dates to actually drag across')
+  const start = await centerOf(firstDate)
+  await page.mouse.move(start.x, start.y)
+  await page.mouse.down()
+
+  for (const isoDate of restDates) {
+    const point = await centerOf(isoDate)
+    await page.mouse.move(point.x, point.y, { steps: 10 })
+    await page.waitForTimeout(50)
+  }
+
+  await page.mouse.up()
+}